Free Space Optical (FSO) communication systems are based on the use of infrared light to transmit information at high speed through the atmospheric channel. Their performance is therefore affected by the characteristics of the atmospheric channel. One of the most widely used methods of compensating for the effects of atmospheric factors is modulation. The main aim of this research is to demonstrate the improvement in FSO link performance using PolSK modulation in a subtropical environment such as Côte d’Ivoire. The performance indicators considered are bit error rate, channel capacity, outage probability and energy efficiency. The mathematical expression of the evolution of each of these indicators as a function of the atmospheric parameters of our environment was determined using the gamma-gamma model. A numerical evaluation of the results obtained was carried out using Matlab software. The results show that PolSK modulation offers the best results in terms of BER reduction, with a BER of the order of 10^{− 11} for an SNR of 50dB, compared with BERs of 10^{− 4} and 10^{− 2) for BPSK and OOK modulations respectively. We obtain a probability of interruption of the order of 10^{− 3} for PolSK modulation compared with 10^{− 2} for BPSK modulation and 10− 1 for OOK modulation. As for the channel capacity, we obtain the same value (4.1458 bit/s) for PolSK and BPSK modulation compared with 3.8181 bit/s for OOK modulation. BPSK modulation, on the other hand, stands out for its excellent energy efficiency.